As the dimensions of semiconductor devices continue to shrink with advances in semiconductor materials and fabrication processes, monitoring and controlling semiconductor fabrication processes by lateral dimensional metrology has become increasingly important in the successful fabrication of advanced semiconductor devices. Currently available systems for lateral dimensional metrology may be configured to perform techniques such as optical, electron beam, ion beam, atomic force, and scanning probe microscopy. In addition, lateral dimensional metrology systems may also perform an electrical metrology technique, e.g., by measuring the resistance of a feature of a known material and determining a cross-sectional area and/or a linewidth of the feature from the measured resistance.
Calibration standards are often used to calibrate lateral dimensional metrology systems. A calibration standard may include features such as lines and/or spaces having a certified lateral dimension. Currently available linewidth calibration standards may have a lateral dimension artifact of approximately 500 nm to approximately 30,000 nm. Such calibration standards may be formed, e.g., by semiconductor fabrication processes such as lithography and etch. Such lithography and etch processes may produce features having a lateral dimension of greater than about 50 nm. As such, a minimum lateral dimension of calibration standards formed by current lithography and etch processes may be limited by a performance capability of such processes and systems. Consequently, lateral dimensional metrology equipment may be calibrated at a minimum lateral dimension substantially greater than a lateral dimension of features formed by advanced semiconductor fabrication processes. Lateral dimensional metrology equipment, therefore, may have limited usefulness for monitoring and controlling advanced semiconductor fabrication processes.
Several calibration methods for lateral dimensional metrology equipment, however, have been developed for use with currently available calibration standards to expand the usefulness of such equipment for advanced processing applications. Examples of such methods are illustrated in U.S. Pat. Nos. 5,914,784 to Ausschnitt et al., 5,969,273 to Archie et al., and 6,128,089 to Ausschnitt et al., and are incorporated herein by reference. Such methods, however, may include indirectly determining a location of an edge of a feature, which may subject the resulting calibration to substantial inaccuracy. In addition, these techniques do not address calibration of metrology systems for measuring angular features such as sidewall angles.
Although the following detailed description contains many specific details for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the exemplary embodiments of the invention described below are set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.